Aqueous dispersions of water-soluble polymers of N-vinyl carboxylic acid amides, method for the production and use thereof

ABSTRACT

Aqueous dispersions of water-soluble polymers of N-vinylcarboxamides contain, based on 100 parts of water,
     (A) from 5 to 80 parts by weight of water-soluble polymer containing N-vinylformamide units and/or N-vinylacetamide units and having particle sizes of from 50 nm to 2 μm and   (B) from 1 to 50 parts by weight of at least one polymeric dispersant which is incompatible with the water-soluble polymers (A) in aqueous solution, which dispersions are prepared by polymerizing   (A) from 5 to 80 parts by weight of N-vinylformamide and/or N-vinylacetamide, if desired together with other monoethylenically unsaturated monomers which form water-soluble polymers therewith, and   (B) from 1 to 50 parts by weight of at least one polymeric dispersant which is incompatible with the polymers, formed from the monomers (A), in aqueous solution,
 
in 100 parts by weight of water, at from 30 to 95° C. in the presence of from 0.001 to 5.0% by weight, based on the monomers used, and the aqueous dispersions of water-soluble polymers are used as drainage aids, flocculants and retention aids and as wet and dry strength agents and as fixing compositions in papermaking.

The present invention relates to aqueous dispersions of water-solublepolymers of N-vinylcarboxamides, processes for their preparation andtheir use in papermaking.

EP-A-01 83 466 discloses a process for the preparation of aqueousdispersions of water-soluble polymers, cationic monomers, for exampledialkylaminoacrylamides quaternized with benzyl chloride, beingpolymerized in an aqueous salt solution in the presence of a polymericdispersant. Dispersants used are, for example, polyols, polyalkyleneethers, alkali metal salts of polyacrylic acid and alkali metal salts ofpoly-2-acrylamido-2-methylpropane-sulfonic acid. Salt concentration inthe polymerization medium is preferably from 15% by weight to thesaturation limit.

DE-A-44 30 069 discloses aqueous, solvent-free dispersions of 20cationic polymers, which are used as sizes for paper. The polymers areprepared by free radical polymerization of cationic monomers, if desiredas a mixture with other monomers in solution or dispersion or by masspolymerization.

DE-A 195 32 229 discloses a process for the preparation oflow-viscosity, water-soluble polymer dispersions. In this process,water-soluble monomers, as a mixture with a crosslinkable N-methylolcompound, or polymerized in aqueous solution in the presence of at leastone polymeric dispersant, the resulting polymer being incompatible withthe dispersant. The dispersions thus obtained are used as flocculants.

WO-A-97/30094 discloses a process for the preparation of dispersions ofwater-soluble cationic vinyl polymers, water-soluble, cationichydrophobically modified vinyl monomers or water-soluble, nonionic,hydrophobic vinyl monomers being polymerized with water-soluble,cationic and/or water-soluble neutral vinyl monomers in aqueous saltsolutions using a water-soluble initiator in the presence of stabilizerswhich consist of a graft copolymer which contains polyethylene oxide asthe grafting base and grafted-on cationic vinyl monomers as side chains.WO-A 97/34933 relates to aqueous dispersions of high molecular weight,nonionic or anionic polymers which were prepared by polymerization ofthe monomers in a saturated salt solution with addition of an anionic,water-soluble polymer stabilizer. Preferably used monomers areacrylamide and acrylic acid.

It is an object of the present invention to provide aqueous dispersionsof water-soluble polymers, which dispersions are virtually free ofstabilizing inorganic salts.

We have found that this object is achieved, according to the invention,by aqueous dispersions of water-soluable polymers of N-vinylformamideand/or N-vinylacetamide if the dispersions contain, based on 100 partsby weight water, 1–10 μm particles of

-   -   (A) from 5 to 80 parts by weight of a water-soluble polymer        containing N-vinylformamide units and/or N-vinylacetamide units        and

-   (B) from 1 to 50 parts by weight of at least one polymeric    dispersant which is incompatible with the water-soluble polymers (A)    in aqueous solution.

The aqueous dispersions of water-soluble polymers preferably contain,based on 100 parts by weight of water,

-   (A) from 10 to 50 parts by weight of a water-soluble polymer 25    containing N-vinylformamide units and/or N-vinylacetamide units and-   (B) from 5 to 40 parts by weight of at least one polymeric    dispersant which is incompatible with the water-soluble 30    polymers (A) in aqueous solution.

Particularly preferred dispersions are those which contain, as component(A), homopolymers of N-vinylformamide. N-vinylformamide units andN-vinylacetamide units can be characterized with the aid of thefollowing formula:

where R is H or CH₃.

The water-soluble polymers containing N-vinylformamide units and/orN-vinylacetamide units can, if required, contain from 1 to 80,preferably from 5 to 30, % by weight of further monomers ascopolymerized units. Such monomers are, for example, monoethylenicallyunsaturated carboxylic acids of 3 to 8 carbon atoms, such as acrylicacid, methacrylic acid, dimethacrylic acid, ethacrylic acid, maleicacid, citraconic acid, methylenemalonic acid, allylacetic acid,vinylacetic acid, crotonic acid, fumaric acid, mesaconic acid anditaconic acid. From this group of monomers, acrylic acid, methacrylicacid, maleic acid or mixtures of said carboxylic acids are preferablyused. The monoethylenically unsaturated carboxylic acids are used eitherin the form of the free acids or in the form of their free alkali metal,alkaline earth metal or ammonium salts in the copolymerization. Forneutralization of the free carboxylic acids, sodium hydroxide solution,potassium hydroxide solution, sodium carbonate, potassium carbonate,sodium bicarbonate, magnesium oxide, calcium hydroxide, calcium oxide,gaseous or aqueous ammonia, triethylamine, ethanolamine, diethanolamine,triethanolamine, morpholine, diethylenetriamine ortetraethylenepentamine is preferably used.

Further suitable monomers are, for example, the esters, amides andnitriles of the abovementioned carboxylic acids, e.g. methyl acrylate,ethyl acrylate, methyl methacrylate, ethyl methacrylate, hydroxyethylacrylate, hydroxypropyl acrylate, hydroxybutyl acrylate, hydroxyethylmethacrylate, hydroxypropyl methacrylate, hydroxyisobutyl acrylate,hydroxyisobutyl methacrylate, monomethyl maleate, dimethyl maleate,monoethyl maleate, diethyl maleate, 2-ethylhexyl acrylate, 2-ethylhexylmethacrylate, acrylamide, methacrylamide, N-dimethylacrylamide,N-tert-butylacrylamide, acrylonitrile, methacrylonitrile,dimethylaminoethyl acrylate, diethylaminoethyl acrylate,diethylaminoethyl methacrylate and the salts of the last-mentioned basicmonomers with carboxylic acids or mineral acids and the quaternizedproducts of the basic (meth)acrylates.

Other suitable copolymerizable monomers are furthermoreacrylamidoglycolic acid, vinylsulfonic acid, allylsulfonic acid,methallylsulfonic acid, styrenesulfonic acid, 3-sulfopropyl acrylate,3-sulfopropyl methacrylate and acrylamidomethylpropanesulfonic acid andmonomers containing phosphoric acid groups, such as vinylphosphonicacid, allylphosphonic acid and acrylamidomethylpropanephosphonic acid.The monomers containing acid groups can be used in the polymerization inthe form of free acid groups and in a form partially or completelyneutralized with bases.

Further suitable copolymerizable compounds are N-vinylpyrrolidone,N-vinylcaprolactam, N-vinylimidazole, N-vinyl-2-methylimidazole,N-vinyl-4-methylimidazole, diallylammonium chloride, vinyl acetate,vinyl propionate and styrene. It is of course also possible to usemixtures of said monomers. The said monomers when polymerized alone donot give water-soluble polymers, the polymers containingN-vinylformamide units and/or N-vinylacetamide units contain thesecomonomers as polymerized units only in amounts such that the copolymersare still water-soluble. In contrast to water-in-oil polymer emulsions,no organic solvents are required for the novel aqueous dispersions. Asis evident from the prior art stated at the outset, concentratedsolutions of inorganic salts are a conventional medium for thepreparation of aqueous dispersions of water-soluble polymers. As aresult, the known dispersions have a very high salt load. Novel aqueousdispersions of water-soluble polymers are in comparison virtuallysalt-free. The aqueous dispersions of water-soluble polymers ofN-vinylformamide and/or N-vinylacetamide preferably have a high polymercontent and preferably contain polymers having high molar masses incombination with low viscosity. The molar masses of the polymerscontaining N-vinylformamide units and/or N-vinylacetamide units are, forexample, from 5·10⁴ to 1·10⁷, preferably from 2·10⁵ to 1·10⁶.

The polymeric dispersants additionally contained as component (B) in theaqueous dispersions differ in the composition from the water-solublepolymers (A) described above. The polymeric dispersant (B) isincompatible with the water-soluble polymer (A). The average molarmasses of the polymeric dispersants are preferably from 1000 to 500,000,in particular from 1500 to 50,000.

The polymeric dispersant containing at least one functional groupselected from ether, hydroxyl, carboxyl, sulfone, sulfate ester, amino,imino, tert-amino and/or quaternary ammonium groups. Examples of suchcompounds are: carboxymethylcellulose, water-soluble starch and starchderivatives, starch esters, starch xanthogenates, starch acetates,dextran, polyalkylene glycols, polyvinyl acetate, polyvinyl alcohol,polyvinylpyrrolidone, polyvinylpyridine, polyethyleneimine,polyvinylimidazole, polyvinylsuccinimide and polydiallyldimethylammoniumchloride.

If the aqueous dispersions of water-soluble polymers ofN-vinylcarboxamides are used in papermaking, polymeric dispersants whichhave further process- or product-improving properties are preferablyused for the preparation of these dispersions. In this way, it ispossible to offer combination solutions to the papermaker. For example,the dispersants (B) of the aqueous dispersions of water-soluble polymersof N-vinylcarboxamides can be selected from compounds which are employedin papermaking as fixing compositions, wet or dry strength agents,dispersants for inorganic solids, antiadhesion compositions for betterrelease from rollers or detackifiers, with the result that the soft,tacky impurities of the paper stock are converted into brittle deposits.In papermaking, it is of course possible to use further processassistants together with the novel aqueous dispersions. For example, apolyacrylamide or polyethylene oxide having retention activity mayadditionally be used with a novel aqueous dispersion ofpoly-N-vinylformamide.

The aqueous dispersions contain from 1 to 50, preferably from 5 to 40,parts by weight, based on 100 parts by weight of water, or at least oneof the abovementioned polymeric dispersants (B).

The present invention also relates to a process for the preparation ofaqueous dispersions of water-soluble polymers of N-vinylformamide and/orof N-vinylacetamide, wherein

-   (A) from 5 to 80 parts by weight of N-vinylformamide and/or    N-vinylacetamide, if desired together with other monoethylenically    unsaturated monomers which form water-soluble polymers therewith,    and-   (B) from 1 to 50 parts by weight of at least one polymeric    dispersant which is incompatible with the polymers, formed from the    monomers (A), in aqueous solution,    in 100 parts by weight of water, are subjected to free radical    polymerization at from 30 to 95° C. in the presence of from 0.001 to    5.0% by weight, based on the monomers used, of polymerization    initiators which form free radicals under the polymerization    conditions.

In the preferred embodiment of the process,

-   (A) from 10 to 50 parts by weight of N-vinylformamide and/or    N-vinylacetamide, if desired together with other monoethylenically    unsaturated monomers which form water-soluble polymers therewith,    and-   (B) from 5 to 40 parts by weight of at least one polymeric    dispersant which is incompatible with the polymers, formed from the    monomers (A), in aqueous solution,    in 100 parts by weight of water, are polymerized at from 40 to    70° C. with from 0.5 to 2.0% by weight, based on the monomers used    in the polymerization, of the azocompounds which decompose into free    radicals under the polymerization conditions.

The monomers are subjected to free radical polymerization according tothe invention, i.e. polymerization initiators which form free radicalsunder the polymerization conditions are used. Suitable compounds of thistype are, for example, hydrogen peroxide, peroxides, hydroperoxides,redox catalysts and nonoxidizing initiators, such as azocompounds whichdecompose into free radicals under the polymerization conditions. Suchazo compounds are, for example, 2,2′-azobis(2-amidinopropane)dihydrochloride, 2,2′-azobis(N,N′-dimethyleneisobutyramidine)dihydrochloride, 2,2′-azobis(2,4-dimethylvaleronitrile,2,2′-azobis[2-methyl-N-(2-hydroxyethyl)propionamide] or2,2′-azobisisobutyronitrile. It is of course also possible to suemixtures of different initiators. A particularly preferred preparationprocess for the aqueous dispersions of water-soluble polymers is one inwhich

-   -   (A) N-vinylformamide, if desired together with other        monoethylenically unsaturated monomers, and    -   (B) polyethylene glycol, polyvinylpyrrolidone or mixtures        thereof        are polymerized at from 40 to 55° C. with water-soluble        azoinitiators. Suitable polymeric dispersants (B) are preferably        polyethylene glycol, polypropylene glycol, copolymers of        ethylene glycol and propylene glycol, polyvinyl acetate,        polyvinyl alcohol, polyvinylpyridine, polyvinylimidazole,        polyvinylsuccinimide, a 1:1 molar ratio copolymer of        N-vinylcaprolactam and N-vinylmethacetamide,        polydiallyldimethylammonium chloride, polyethyleneimine and        mixtures thereof. The molar masses of these polymers are        preferably from 1500 to 50,000.

If polymer dispersions and polymers having low molecular weights aredesired, it is possible, for example, to increase the amounts ofinitiator which are usually used in the polymerization so that it isalso possible to use amounts of initiator which are outside theabovementioned range for the amounts of initiator. Aqueous dispersionsof low molecular weight homo- and copolymers of the suitablevinylcarboxamides can also be obtained by carrying out thepolymerization in the presence of polymerization regulators and, ifrequired, simultaneously using a larger amount of initiator than thatusually required. Suitable polymerization regulators are, for example,compounds containing sulfur in bound form, such as dodecyl mercaptan,thioglycolic acid, thioacetic acid and mercaptoalcohols, such asmercaptoethanol, mercaptopropanols and mercaptobutanols. In addition,formic acid, isopropanol and hydrazine in the form of salts with strongacid may also be used as polymerization regulators.

The molecular weights of the polymers resent in dispersed form can alsobe characterized with the aid of the K values according to Fikentscher.The K values are up to 300 and preferably in the range from 130 to 180.From light scattering experiments, it follows that a K value of 250corresponds to an average molecular weight of the polymers of about7,000,000 dalton.

By eliminating formyl groups from polymers containing N-vinylformamideunits and by eliminating the group CH₃—CO— from polymers containingN-vinylacetamide units, polymers containing vinylamine units are formedin each case. Elimination may be effected partially or completely. Ifthe hydrolysis is carried out in the presence of acids, the vinyamineunits of the polymers are present as ammonium salts. The hydrolysis canalso be carried out with the aid of bases, for example of metalhydroxides, in particular of alkali metal and alkaline earth metalhydroxides. Preferably, sodium hydroxide or potassium hydroxide is used.In particular cases, hydrolysis can also be carried out with the aid ofammonia or amines. In the case of the hydrolysis in the presence ofbases, the vinylamine units are present in the form of free bases.

Suitable hydrolysis agents are preferably mineral acids, such as halogenhalides, which may be used in gaseous form or as an aqueous solution.Concentrated hydrochloric acid, sulfuric acid, nitric acid or phosphoricacid and organic acids, such as C1- to C5-carboxylic acids, andaliphatic or aromatic sulfonic acid are preferably used. For example,from 0.05 to 2, in particular from 1 to 1.5, molar equivalents of acidare required per equivalent of formyl groups in the polymers containingpolymerized N-vinylformamide units. Hydrolysis of the N-vinylformamideunits takes place significantly more rapidly than that of the polymershaving N-vinylacetamide unite. If copolymers of the suitablevinylcarboxamides with other comonomers are subjected to the hydrolysis,the comonomer units contained in the copolymer can also be chemicallymodified. For example, vinyl alcohol units are formed from vinyl acetateunits. In hydrolysis, acrylic acid units are formed from methyl acrylateunits, and acrylamide or acrylic acid units are formed fromacrylonitrile units. The hydrolysis of the N-vinylformamide units and/orvinylacetamide units of the polymers (A) can be carried out to an extentof from 5 to 100%, preferably from 10 to 40%. Although aqueousdispersions of water-soluble N-vinylcarboxamides dissolve on dilutionwith water, the dispersion is surprisingly not destroyed duringhydrolysis. The particle diameter of the hydrolyzed particles before andafter the hydrolysis is from 1 to 10 μm.

The dispersions described above, i.e. the unhydrolyzed as well as thehydrolyzed aqueous dispersions of water-soluble N-vinylcarboxamides, areused as drainage aids, flocculants and retention aids and as wet and drystrength agents and as fixing compositions in papermaking. The cationicpolymers can moreover be used as flocculants for wastewaters in thedewatering of sewage sludge, as flocculants in ore dressing and intertiary oil production or as dispersants, for example, for inorganicand organic pigments, dyes, cement or crop protection agents. Theunhydrolyzed as well as the hydrolyzed aqueous dispersions can moreoverbe used as strength agents for paper, as fixing compositions for solubleand insoluble interfering substances in papermaking and as compositionsfor paper coating. They can furthermore be used as coating material forfertilizers and crop protection agents and as floorcare compositions.Said aqueous hydrolyzed and unhydrolyzed polymer dispersions can also beused in cosmetics, for example for hair formulations, for exampleconditioners, hairsetting compositions or conditioners for skincarecompositions and as thickeners for cosmetic formulations and furthermoreas a component of cosmetic formulations for oral hygiene.

The K values were determined according to H. Fikentscher,Cellulose-Chemie, 13 (1932), 58–64 and 71–74, in aqueous solution at 25°C. and at a concentration which, depending on the K value range, of from0.1 to 5% by weight. The viscosity of the dispersion was measured ineach case in a Brookfield viscometer using a no. 4 spindle at 20 rpm andat 20° C. The data in % are percentages by weight.

EXAMPLE 1

800 g of water, 5 g of sodium dihydrogen phosphate dihydrate, 150 g ofpolyvinylpyrrolidone (K value 30, determined in 1% strength aqueoussolution) and 150 g of polyethylene glycol having a molar mass of 1500were weighed into a 2 l glass vessel equipped with an anchor stirrer,nitrogen supply line, distillation bridge and reduced pressureregulating means were all processed by stirring to give a homogeneoussolution. 500 g of N-vinylformamide were added and the pH of thesolution was then brought to 6.5 by adding 25% strength aqueous sodiumhydroxide solution. Nitrogen was passed continuously through thereaction mixture, and a solution of 2.5 g of2,2′-azobis-(2-aminopropane) dihydrochloride in 100 g of water was addedand the reaction mixture was heated to 50° C. for polymerization. Thepolymerization was carried out at this temperature and 130 mbar, theresulting heat of polymerization being removed by evaporative cooling.The polymerization time was 13 hours. Within this time, water wasdistilled off in an amount such that an aqueous dispersion having asolids content of 44% was obtained. It had a viscosity of 15600 mPas, aK value of 140 (measured as 0.1% strength solution in 5% strengthaqueous NaCl solution) and a residual N-vinylformamide monomer contentof 0.1%.

EXAMPLE 2

1200 g of water, 5 g of sodium dihydrogen phosphate dihydrate, 150 g ofpolyvinylpyrrolidone (K value 30, determined in 1% strength aqueoussolution) and 150 g of polyethylene glycol having a molar mass of 1500were initially taken in a 2 l glass vessel equipped with an anchorstirrer, nitrogen supply line, distillation bridge and reduced pressureregulating means. The mixture was stirred, and 643 g of N-vinylformamidewere added. The pH of the reaction mixture was brought to 6.5 by adding25% strength aqueous sodium hydroxide solution. Nitrogen was passedcontinuously through the reaction mixture and 2.5 g of2,2′-azobis(2-aminopropane) dihydrochloride in the form of a solution in100 g of water were added and the batch was heated to a polymerizationtemperature of 50° C. The polymerization was carried out at 130 mbar,the resulting heat of polymerization being removed in the course of 13hours by evaporative cooling and water being distilled off from thereaction mixture in an amount such that an aqueous dispersion having asolids content of 44.1% and a polyvinylformamide fraction of 25% wasobtained. The viscosity of the aqueous dispersion was 5800 mpas. The Kvalue of the polymer was 148 and the residual N-vinylformamide monomercontent was 0.2%.

EXAMPLE 3

In the apparatus described in Example 1, first a solution of 1200 g ofwater, 5 g of sodium dihydrogen phosphate dihydrate, 150 g ofpolyvinylpyrrolidone (K value 30, measured in 1% strength aqueoussolution) and 150 g of polyethylene glycol having a molar mass of 1500was prepared, and then 500 g of N-vinylformamide were added and a 25%strength aqueous sodium hydroxide solution was added in an amount suchthat the pH of the solution was 6.5. Nitrogen was passed continuouslythrough the solution, and an aqueous solution of 2.5 g of2,2′-azobis-(2-aminopropane) dihydrochloride in 100 g of water was addedand the mixture was heated to 50° C. The polymerization was carried outat 130 mbar in the course of 13 hours, water being distilled off forevaporative cooling in an amount such that an aqueous polymer dispersionhaving a solids content of 41.0% was obtained. The viscosity of thedispersion was 3075 mPa.s. The proportion of dispersedpolyvinylformamide was 20%. The polymer had a K value (measured as 0.1%strength solution in 5% strength aqueous NaCl solution) of 138 and aresidual monomer content of 0.2%.

EXAMPLE 4

In the apparatus stated in Example 1, the solution of 1044 g of water, 5g of sodium dihydrogen phosphate dihydrate, 200 g of a partiallyhydrolyzed polyvinyl acetate having a degree of hydrolysis of 86% and100 g of polyethylene glycol having a molar mass of 1500 was preparedand 500 g of N-vinylformamide were added while stirring. The 25%strength aqueous sodium hydroxide solution was then added in an amountsuch that the pH was 6.5. Nitrogen was passed through the reactionmixture, and a solution of 2.5 g of 2,2′-azobis(2-aminopropane)dihydrochloride, dissolved in 1000 g of water, was added and thereaction mixture was heated to a polymerization temperature of 50° C.The polymerization was carried out at 130 mbar over a period of 13 hoursand with removal of the heat of polymerization by evaporative cooling.Water was distilled off in an amount such that an aqueous dispersionhaving a solids content of 36% was obtained. The polymer had a K value(measured at a polymer concentration of 0.1% in 5% strength aqueous NaClsolution) of 130 and a residual monomer content of 0.1%. The particlediameter of the dispersed particles was 200 nm.

EXAMPLE 5

In the apparatus stated in Example 1, first an aqueous solution wasprepared by initially taking therein 836 g of water, 5 g of sodiumdihydrogen phosphate dihydrate, 150 g of a copolymer ofN-vinylcaprolactam and N-vinylmethylacetamide in a molar ratio of 1:1,having a molar mass of 45,000, and 150 g of polyethylene glycol having amolar mass of 1500, adding 500 g of N-vinylformamide while stirring andbringing the pH of the solution to 6.5 by adding 25% strength aqueoussodium hydroxide solution. Nitrogen was then passed continuously throughthe mixture, a solution of 2.5 g of 2,2′-azobis(2-aminopropane)dihydrochloride in 100 g of water was added and the mixture was heatedto 50° C., at which the polymerization was carried out. At the sametime, a pressure of 130 mbar was established, and the resulting heat ofpolymerization was removed by rapid cooling. For this purpose, water wasdistilled off over a period of 13 hours in an amount such that anaqueous polymer dispersion having a solids content of 43% was formed.The polyvinylformamide content was 26.9%. The aqueous solution had aviscosity of 8700 mPa.s. The polymer had a K value (measured in 5%strength aqueous NaCl solution at a polymer concentration of 0.1%) of110.2 and a residual N-vinylformamide monomer content of 0.2%. Theparticle size of the dispersed particles was 200 nm.

EXAMPLE 6

216.7 g of the aqueous polymer dispersion prepared according to Example1 were initially taken in a 3-necked flask which had a capacity of 250ml and was equipped with a gas inlet tube, reflux condenser and stirrer.4 g of gaseous hydrogen chloride were passed in while stirring in thecourse of 10 minutes. The reaction mixture was heated to 50° C. andstirred for 5 hours at this temperature. Thereafter, the degree ofhydrolysis for the polymer was 10.1%, i.e. the polymer contained 10.1%of vinylamine units. The reaction mixture was neutralized by passing in2.2 g of ammonia gas. The pH was 7.5. The dispersion had a viscosity of16,600 mPa.s. The mean particle size of the dispersed particles was 250nm. The polymer had a molar mass of 900,000 daltons.

EXAMPLE 7

206 g of the aqueous dispersion prepared according to Example 3 wereinitially taken in a 3-necked flask having a capacity of 250 ml andequipped with a gas inlet tube, reflux condenser and stirrer. 20.3 g ofhydrogen chloride gas were then passed in while stirring in the courseof 25 minutes. The reaction mixture was heated to 75° C. and thenstirred for 2 hours at this temperature. The degree of hydrolysis of thepoly-N-vinylformamide was 75%. The dispersion had a viscosity of 7040mPa.s. The particle size of the dispersion was 300 nm. The molar mass ofthe polymer was 500,000 daltons.

EXAMPLE 8

212 g of the dispersion obtained according to Example 3 were initiallytaken in a 3-necked flask having a capacity of 250 ml. 2.8 g of gaseoushydrogen chloride were then passed in while stirring, and the reactionmixture was heated to 50° C. The mixture was then stirred for 6.5 hoursat this temperature. Thereafter, the degree of hydrolysis of the polymerwas 8.5%. The aqueous dispersion had a viscosity of 4800 mPa.s. Theparticle size of the dispersed particles was 200 nm. The polymer had amolar mass of 1.2·10⁶ daltons.

EXAMPLE 9

217.8 g of the polymer dispersion prepared according to Example 3 wereinitially taken in a 3-necked flask having a capacity of 250 ml. 8 g ofgaseous hydrogen chloride were then passed in while stirring, and thereaction mixture was heated to 50° C. The mixture was then stirred for 7hours at this temperature. Thereafter, the degree of hydrolysis of thepolymer was 27.4%. The aqueous dispersion had a viscosity of 4950 mPa.s.The particle size of the dispersed particles was 370 nm and the molarmass was 1.07·10⁶ daltons.

In the Examples 1 to 4, the concentration of sodium dihydrogen phosphatedihydrate by weight based on the amount of water in the initial reactionmixture, to which the initiator is added is 0.63% (Example 1), 0.42%(Examples 2 and 3), 0.48% (Example 4), and 0.60% (Example 5). Afteraddition of the initiator in water, the sodium dihydrogen phosphateconcentration in percent by weight based on the amount of water is 0.56%(Example 1), 0.38% (Example 2), 0.38% (Example 3), 0.24% (Example 4) and0.53% (Example 5).

Use Examples

Determination of the Drainage Time

The drainage term was determined in a Schopper-Riegler-tester bydraining therein 1 l of the fibrous stock suspension to be tested and ineach case determining the drainage time after the passage of 700 ml ofwater.

Optical Transmittance of the White Water

The optical transmittance of the white water is a measure of retentionof crills and fillers. It was determined with the aid of a photometerand stated in percent. The higher the value for the opticaltransmittance, the better is the retention. The following startingmaterials were used:

The polymers I and II served for comparison with the prior art.

Polymer I:

Polyamidoamine obtained from adipic acid and diethylenetriamine graftedwith ethyleneamine and crosslinked with an α,ω-dichloropolyethyleneglycol ether (cationic drainage aid and retention aid according to U.S.Pat. No. 4,144,123).

Polymer II:

Commercial cationic copolymer of 70% acrylamide and 30% ofdimethylaminoethyl acrylate chloride, K value of the copolymer 250.

Polymer III:

Commercial cationic polyacrylamide (Praesterat® K 350)

Polymers to be Used According to the Invention:

Polymer IV:

Aqueous dispersion which was obtained according to Example 8 (copolymerof 91.5% of N-vinylformamide units and 8.5% of vinylamine units).

EXAMPLE 10

A pulp having a consistency of 2 g/l was prepared from deinkedwastepaper, and 0.2 g/l of china clay was additionally added to thestock. In the Examples 1 to 4, the concentration of sodium dihydrogenphosphate dihydrate by weight based on the amount of water in theinitially reaction mixture is 0.63% (Example 1), 0.42% (Examples 2 and3), 0.48% (Example 4), and 0.60% (Example 5). After addition of theinitiator in water, the sodium dihydrogen phosphate concentration inpercent by weight based on the amount of water is 0.56% (Example 1),0.46% (Example 2), 0.38% (Example 3), 0.25% (Example 4) and 0.53%(Example 5). The paper stock had a pH of 7. First the drainage rate andthen the optical transmittance of the white water were determined. Zerovalue of the drainage time was 79 seconds. The polymers stated in Tables1 and 2 were then added in amounts of 0.02, 0.04 and 0.08%, based on dryfiber, to the fiber suspension and the drainage times and the opticaltransmittance of the white waters were determined. The results shown inTables 1 and 2 were determined.

Drainage time [s] Addition [%] of the polymer to the paper 0.02 0.04stock 0.08 Polymer I 55 40 28 Polymer II 33 25 18 Polymer III 43 32 23Polymer IV 39 30 23

Optical transmittance [%] to the paper Addition [%] of the polymer stock0.02 0.04 0.08 Polymer I 51 63 77 Polymer II 73 86 93 Polymer III 62 7586 Polymer IV 67 74 83

1. An aqueous dispersion of a water-soluble polymer of N-vinylformamideand/or of N-vinylacetamide, wherein the dispersion contains, based on100 parts by weight of water, 1–10 μm particles of: (A) from 5 to 80parts by weight of a water-soluble polymer containing N-vinylformamideunits and/or N-vinylacetamide units, and (B) from 1 to 50 parts byweight of at least one polymeric dispersant which is incompatible withthe water-soluble polymer (A) in aqueous solution, wherein saiddispersion is substantially free of stabilizing inorganic salt.
 2. Anaqueous dispersion of a water-soluble polymer as claimed in claim 1,wherein the dispersion contains, based on 100 parts by weight of water,(A) from 10 to 50 parts by weight of a water-soluble polymer containingN-vinylformamide units and/or N-vinylacetamide units and (B) from 5 to40 parts by weight of at least one polymeric dispersant.
 3. An aqueousdispersion of a water-soluble polymer as claimed in claim 1, wherein thedispersion contains as component (A) a homopolymer of N-vinylformamide.4. An aqueous dispersion of a water-soluble polymer as claimed in claim1, wherein the N-vinylformamide units and/or vinylacetamide units of thepolymer (A) have been partially or completely converted into a polymercontaining vinylamine units by hydrolysis with acids or bases.
 5. Anaqueous dispersion of a water-soluble polymer as claimed in claim 1,wherein said at least one polymeric dispersant is selected from thegroup consisting of carboxymethylcellulose, water-soluable starch,starch esters, starch xanthogenates, starch acetates, dextran,polyalkylene glycols, polyvinyl acetate, polyvinyl alcohol,polyvinylpyrrollidone, polyvinylpyridine, polyethyeneimine,polyvinylimidazole, polyvinylsuccinimide, a 1:1 molar ratio copolymer ofN-vinylcaprolactam and N-vinylacetamide, polydiallyldimethylammoniumchloride, and mixtures thereof.